Liquid feeding apparatus



Dec. 27, 1955 w, SMART ET AL LIQUID FEEDING APPARATUS 2 Sheets-Sheet 1 Filed May 24, 1954 T a m mo" mwA m m W n TM 0 mm H w A m Dec. 27, 1955 w. L. SMART ET L LIQUID FEEDING APPARATUS 2 Sheets-Sheet 2 Filed May 24, 1954 w mi umm

INVENTORS ROBERT 0. JUV/NALL 8 WILLIAM L. SMART fbacmm/ Altar/lays United States Patent LIQUID FEEDING APPARATUS William L. Smart and Robert C. Juvinall, Indianapolis,

Ind., assignors to Ransburg Electra-Coating Corp., Indianapolis, Ind., a corporation of Indiana Application May 24, 1954, Serial No. 431,768

12 Claims. (Cl. 299-63) Our invention relates to apparatus for feeding liquid from a stationary means to a rotating means, particularly for feeding liquid coating material from a stationary feed tube to a rotating atomizing device.

Numerous industrial processes require that a liquid be fed from a stationary member to a moving member without appreciable loss or leakage of the liquid from its desired path of flow. For example, in the electrostatic spray coating of articles of manufacture it has been found particularly desirable to feed liquid coating material from a stationary reservoir to a rotating atomizing device such as a flat disc or flaring bell for atomization therefrom and electrostatic deposition on the articles. Where the atomizing device is being used to spray in a generally horizontal or an upwardly direction, proper feeding of the liquid coating material to the rotating device has presented a number of problems.

It is well known that certain liquid coating materials, particularly some pigmented paints, have extremely abrasive qualities and that on exposure to air most liquid coating materials leave a gummy residue. Moreover, liquid coating materials generally contain solvents which readily attack the materials used in conventional liquid sealing devices. These qualities make the useful life of conventional sealing devices very short. Once the liquid coating material leaks past its seal, its abrasive and gummy qualities will quickly render the bearing structure and other moving parts of the rotating atomizing device unserviceable. It is therefore desirable in feeding liquid coating material to such a device that conventional mechanical seals and related packings be eliminated and that steps be taken to insure that liquid coating material does not reach the bearing structure.

The problem of feeding liquid coating material to a rotating atomizing device is further complicated by the fact that a very steady, laminar flow is required. Spurting and other forms of turbulence in the transfer of the liquid from the stationary member to the rotating member tends to produce slugging; that is, turbulence in the liquid transfer often causes droplets or slugs" of liquid which are too large for commercial spray coating to be discharged from the rotating atomizing device and deposited on the articles being coated. Slugging may ruin the appearance of the coated article and necessitate its rejection and complete refinishing. This, of course, is costly and to be avoided.

Our invention is directed to providing means for feeding liquid from a stationary to a rotating member in a steady, laminar flow and without the use of conventional.

packings or liquid sealing devices. We have discovered an eificient liquid feeding device for use in an electrostatic coating system or the like which comprises a rotatable hollow shaft and an annular-edged atomizing device mounted for rotation on one end of the shaft having an extended liquid-guiding surface which leads to the atomizers annular atomizing edge. A stationary feed device generally in the form of a tube extends through the shaft terminating in an annular liquid discharge edge of 2,728,606 Patented Dec. 27, 1955 knife-like sharpness which is closely and equally spaced from the liquid-guiding surface of the atomizer. Preferably the discharge edge is spaced not more than .05 inch from the liquid-guiding surface. When the shaft and atomizer are rotated and liquid is fed at a controlled rate through the stationary feed tube the liquid will flow without turbulence through the tube and over its liquid discharge edge to the liquid-guiding surface of the rotating atomizer to form an expanding liquid film for atomization from the edge of the atomizer.

An object of our invention is to provide improvements in a rotary liquid utilization device for the protection of the bearing structure and other movable parts of the device. Another object is to provide a more efiicient means for feeding liquid coating material and the like generally upwardly or horizontally to a rotating atomizing device.

Means for accomplishing the above stated and related objects of our invention will now be described in detail with reference to the accompanying drawings in which:

Fig. 1 is a partially broken away elevational view of one type of atomizing device embodying a form of our invention;

Fig. 2 is a detailed view of the stationary feed tube shown in Fig. 1;

Fig. 3 is a partially broken away elevational view of a second type of atomizing device utilizing another embodiment of our invention; and

Fig. 4 is a detailed view of the stationary feed tube shown in Fig. 3.

Our invention is particularly adapted for use in feeding liquid coating material to a rotating atomizer used in an electrostatic coating system. The invention may, however, assume many forms and for convenience of illustration there are shown in the drawings and will now be fully described two specific embodiments of our invention in an electrostatic coating system which are illustrative of the principles of the invention. The scope of the invention, however, is not to be limited by the following description.

Referring first to Figs. 1 and 2 there is shown an annular-edged atomizing device 10 which includes an atomizing disc and hub assembly (hereinafter called a disc) 11 on the upper end of a rotatable hollow shaft 12. The disc and shaft are rotated by an integral motor assembly lying within a housing 13 whose details are not shown as our invention is independent of the motor or other driving means for shaft 12 and disc 11.

Shaft 12 extends axially through housing 13. Beneath the lower end of rotatable shaft 12 and affixed to housing 13 is a stationary tube support 15 having an axial passageway concentric with shaft 12 and disc 11. A stationary feed device or tube 16 is securely mounted concentrically within the passageway of stationary tube support 15 by means of a set screw 18 and sealed by an O-ring 19 of flexible material. Due to the close tolerances required between the upper portion of tube 16 and the surface of disc 11 the tube must be firmly positioned and thus set screw 18 is located to bear against the middle of the lower collar of tube 16 with a substantial area of the collar snugly fitted against tube support 15 both above and below the set screw.

A back plate 20 having an axial passageway communicating with stationary feed tube 16 is securely mounted on the lower end of stationary tube support 15. Liquid coating material to be atomized is fed from a reservoir 22 at acontrolled rate by a supply tube 21 upwardly through the passageway in back plate 20 to the interior of feed tube 16. Atomizing device 10 may be maintained at high electrical potential by connection to a high voltage source 24 as shown or other means known to the art employed to elfect a particle-depositing potential difference between the atomized coating material and the articles. Th'isis generally accomplished by maintaining'th'e articles and their supports at a dilference of potential from the atomizer, preferably by groundingthe articles-and:main--' out turbulence to disc 11, stationary feed device16has.

an upper dome-like portion terminating. in anannular liquid'discharge edge 16a-over which the liquid coating material llows for transference to the upper. surface of the disc where centrifugal force will cause the liquid-to spread into an outwardly moving thin film for atomization from the annular edge of the disc.

also by making edge 16a relatively sharp or knife-like.-

it was also found desirable that edge 16a lie at least as close to the upper surface of the disc as does any other portion of tube 16. In the embodiment shown this is done by providing a surface 16b extending inwardly from edge 16a substantially parallel to the surface of disc 11.

In order to prevent the further movement of any liquid coating material which might creep beyond edge 16a and surface 16b and inwardly along the under surface of the dome, a downwardly depending drip skirt 16c was formed on the underside of the dome-like upper portion of feed tube 16. Preferably drip skirt 160 has a lower edge of knife-like sharpness. The lower edge of the drip skirt should extend no lower than the plane of liquid discharge edge 16a and preferably is somewhat above such plane. To further prevent liquid movement along the surface of the disc toward its axis, disc 11 may include an upstanding vertical extension or liquid dam 11a extending upwardly from the horizontal surface of the disc beneath the dome-like upper portion of feed tube 16. I

In certain spray coating operations it is desirable to tilt the disc so that the axis of atomizer is not necessarily vertical but may be at an angle of as much as 45 to the vertical. Feed tube 16 as shown will perform satisfactorily in such attitudes, even though in such inclined attitudes liquid will be transferred to the disc from.

only the lowermost segment of tube edge 16a. Preferably, in order to provide for supported liquid flow along the upper surface of the dome to the disc, the upper surface of the domed portion of the feed tube is at an angle of approximately 40 to the surface of the disc, that is, a line in the direction of liquid flow on the upper surface of the dome over which liquid flows to discharge edge 160 will intersect the liquid-guiding upper surface Such an surface to prevent drying and this is customarily doneby wiping the upper surface of the disc with a solventsoaked rag. operation can in no way reach the hearings or. other interior moving parts of atomizing device 10" because of the umbrella effect of the dome-like upper portionofstationary feed tube 16 and the physical barriers of It was found, however, that there is a tendency for a portion of the Excess solvent and paint from this wiping.

4. drip skirt 16c and dam 11a. Thus the use of stationary tube 16'affords'protection to the bearing structure of the atomizing device both when the device is rotating and stationary.

One commonly used atomizing device embodying our invention includes a flat disc on the upper end of a rotatable hollow shaft having an inner diameter of approximately 0.75 inch. Various coating operations carried on with this device require liquid to be fed generally upwardly to the surface of the atomizing disc at rates of from 15 to 900 cubic centimeters per minute. The disc may be rotated at speeds of from several hundred to several thousand revolutions per minute. A tube constructed in the form of stationary feed tube 16 was able to feed liquidcoating material to the upper surface of the disc at deliveries and speeds within the above ranges and to effect transfer of the liquid smoothly and evenly without a tendency to produce slugging or other undesirable characteristics.

When used with a hollow shaft having an inner' diameter of 0.75 inch, the inner diameter of the lower portion of feed tube 16 is approximately 0.25 inch. The

dome-like upper portion of the tube is smoothly. formed: with the upper surface of the tube, which terminates in liquid discharge edge 16a, making an angle ofapproximately 40" with the upper surface of the disc. uid discharge edge 16a, formed by the intersection of the upper dome-like surface of the tube and surface 16b is relatively sharp. Circular edge 16.2 has a diameter of' about two inches.

fiow. Drip skirt 160 has a diameter of'approximately 1.25'inches and its knife-like lower edge is spaced approximately .03 inch above surface 16b. Dam 11a extends vertically approximately 0.5 inch abovethe upper surface of disc 11.

In order to fit feed tube 16 into its position witlrzthe proper spacing between the upper surface of disc 11 and the surface 16b of the feed tube, uppermost inner portio'n'16d of feed tube 16 is threaded as shown. A' suitablepositioning tool having a threaded element can thus be screwedinto threaded portion 16d of the feed tube tohold it for insertion downwardly through shaft 12 ond type of atomizing device which includes a liar-- ing atomizing bell 31 mounted on one end of a gen-. erally 'horizontalrotatable hollow shaft 32 by an O-ring. 33 and a set screw 34. Bell 31 has an inner liquid? guiding. surface with an innermost conical throatpor-.- tion'31a extending outwardly from the juncture of bell 31 and shaft 32 toward the bells annular edge at an angle of approximately 15 to the axis of the bell and The bell and shaft are rotated by an integral shaft.

motor assembly lyingwithin atomizer housing 35 whose details are notshown as our invention is independent of the motor or other driving means for bell' 31 and shaft 32.

Shaft 32 extends axially through housing 35. At its opposite'end there is affixed to housing 35 a stationary tube'support'36 having an axial passageway concentric with the shaft. A hollow cylindrical tube stop 37 is positioned within the passageway in tube support 361by a set screw 37a; A stationary feed tube .38 is securely mountedco'ncentricall'y, within the passageway in stationary tube support .36 with its-one end against tubestop 37 by, means of a set screw 39 and sealed by an O-ring 40 offlexible material. A'back plate 41 having an axial passageway;

Surface 16b extends parallel to the upper surface of the disc a distance of approximate: ly 0.1 inch measured radially in the direction of liquid communicating with the passageway in tube support 36 is securely mounted on the open face of the stationary tube support. Liquid coating material to be atomized is fed from a reservoir 44 at a controlled rate by a supply tube 45 through the passageway in back plate 41 and through tube stop 37 to the interior of feed tube 38. Atomizing device is maintained at a high electrical potential by connection to a high voltage source 46 as shown.

Fig. 4 shows the details of stationary feed tube 38 with its forward liquid discharging portion shown in crosssection. In order to properly feed liquid coating material to the inner surface 31a of hell 31, stationary feed tube 38 terminates in a forward portion having a flat disc-like surface 38a which lies substantially normal to the axis of the feed tube. Surface 38a terminates in an annular liquid discharge edge 38b preferably of knife-like sharpness which lies closely adjacent to the inner surface of the bell. On the opposite surface of the tube from surface 38a is a cylindrical knife-edge projection or drip skirt 38c extending rearwardly toward shaft 32. When the stationary feed tube is properly assembled within atomizer 30 its edge 38b lies concentric with the throat-like interior surface 31a of the bell and spaced less than .05 inch from surface 31a.

In order to further prevent liquid coating material from reaching the bearing structure of atomizer 30 a cylindrical sleeve or liquid dam 47 is pressed into the throat of bell 31. Liquid darn 47 is concentric with bell 31, shaft 32 and feed tube 38. It extends forwardly into the central passageway formed by surface 31a of the bell so its foremost end lies beneath the knife-edge of drip skirt 38c. Thu; any liquid creeping back along surface 31a toward shaft 32 will be stopped by dam 47. The dam will also tend to prevent any liquid dripping from the edge of drip skirt 380 from reaching the interior of the atomizer.

One commercially used atomizing device of the type shown in Fig. 3 which embodies our invention includes a rotating hollow shaft having an inner diameter of approximately 0.75 inch and a bell in which surface 31a makes an angle of approximatey With the axis of the bell and shaft. Various coating operations using this atomizing device require liquid to be fed generally horizontally to surface 31a of the atomizing bell at rates of from 15 to 900 centimeters per minute. The bell may be rotated at speeds of from several hundred to several thousands of revolutions per minute. A tube in the form of stationary feed tube 38 will feed liquid coating material to inner surface of the bell at deliveries and speeds within the above rangesand effect transfer of the liquid smoothly and evenly without slugging or other undesirable characteristics.

When the hollow shaft has an inner diameter of 0.75 inch and surface 31a inclined at an angle of 15, the inner diameter of feed tube 38 is approximately 0.25 inch. Liquid discharge edge 38b of the tube is of knife-like sharpness and has a diameter of approximately 1.2 inches. Edge 38b is formed by the intersection of two surfaces which make the angle of edge 38b approximately 10. Drip skirt 380 has a diameter of about one inch and extends approximately 0.3 inch rearwardly from surface 38a. Liquid dam 47 is approximately 1 inch in length and extends within the recess formed between the wall of stationary tube 38 and drip skirt 38c as shown. Like tube 16, feed tube 38 is threaded at 38d for ease of insertion and removal from the atomizer.

We claim:

1. In an electrostatic spray coating system, a device for feeding liquid coating material comprising a rotatable hollow shaft, an annular-edged atomizer concentrically mounted for rotation on one end of said shaft, said atomizer having an extended liquid-guiding surface leading to its annular edge, a stationary feed tube extending through said hollow shaft and terminating in a sharp annular liquid discharge edge closely spaced from the extended surface of said atomizer, said discharge edge being concentric with and substantially equally spaced from the liquid-guiding surface of said atomizer, means for rotating said shaft and atomizer about their axes, and means for feeding liquid at a controlled rate to said feed tube for flow therethrough and over its liquid discharge edge to the liquid-guiding surface of the rotating atomizer to form thereon an expanding liquid film for atomization from the edge of said atomizer.

2. In an electrostatic spray coating system, a device for feeding liquid coating material comprising a rotatable hollow shaft, an annular-edged atomizer concentrically mounted for rotation on one end of said shaft, said atomizer having an extended liquid-guiding surface leading to its annular edge, a stationary feed tube extending through said hollow shaft and terminating in a sharp annular liquid discharge edge closely spaced from the extended surface of said atomizer, said discharge edge having a diameter of approximately two inches concentric with and substantially equally spaced from the liquidguiding surface of said atomizer and lying at least as close to said liquid-guiding surface as does any other portion of the feed tube, means for rotating said shaft and atomizer about their axis, and means for feeding liquid at a controlled rate to said feed tube for flow therethrough and over its liquid discharge edge to the liquid guiding surface of the rotating atomizer to form thereon an expanding liquid fihn for atomization from the edge of said atomizer, a line in the direction of liquid flow on the surface of said feed tube over which liquid flows to the liquid discharge edge of the stationary feed tube intersecting the liquid-guiding surface of the atom izer at an angle of approximately 40.

3. Apparatus as set forth in claim 1 wherein the feed tube terminates in a dome-like portion and includes a knife-edged drip skirt on the underside of said dome-like portion within the annular liquid discharge edge of the feed tube. V

4. Apparatus as set forth in claim 3 wherein the rotating atomizer includes a liquid dam extending upwardly from the liquid-guiding surface of the atomizer beneath the dome-like portion of the feed tube beyond the edge of the drip skirt, on the under side of said dome-like portion.

5. Apparatus as set forth in claim 4 wherein the angle between the liquid-guiding surface of the atomizer and the outer dome-like surface of the feed tube adjacent the liquid discharge edge of said feed tube is approximately '6. Apparatus as set forth in claim 1 wherein the stationary feed tube includes a generally cylindrical knifeedged drip skirt lying adjacent to the liquid discharge edge of the feed tube, and the rotating atomizer includes a liquid dam projecting from the liquid-guiding surface of the atomizer and surrounded by the knife edge of the drip skirt.

7. An atomizing apparatus comprising a housing enclosing an electric motor having a rotatable hollow shaft, an annular-edged atomizer mounted for rotation on one end of said shaft, said atomizer having an extended liquidguiding surface, a removable stationary feed tube extend' ing concentrically through said shaft and terminating at: one end in a liquid discharge edge lying closely adjacent the liquid-guiding surface of said atomizer, a portion of the inner surface of the feed tube being threaded, a stationary tube support afiixed to said housing maintained in fixed spaced relation to the end of said shaft opposite said atomizer, an O-ring of resilient material mounted concentrically in an annular groove in the outer surface of said stationary feed tube, said O-ring being positioned to fit snugly against saidtube support, a set screw positioned radially within said tube support, the end of said stationary tube opposite said liquid discharge edge being positioned within said tube support and firmly held by said set screw, said feed tube being removable from said apparatus by loosening said set screw, fitting a threaded 7 tool into the threaded portion of said feed tube'and draw-f ing-the feedtube axially out of said hollow 'sliaftl 8. An atomizing apparatus comprising a; rotatable; hollow shaft a bell-shaped atomizermounted tor-rota:-

face portion flaring outwardly at an angle to'th'e aXisof said shaft and bell ofapproximately 15;aholloW'stationary feed device extendingconcentricallythrough said shaft andterminating-at one end in asharp annular liquid 8 said*liquidldischarge edgeto' the inner surface' of the rotatingib'ell. V

l L-ln' an'electrostatic spray coating'system, a device tot-"feeding liquid coating material comprising a rotatable tion on-said shaft, said atomizer having an interior SDI? heliew shaft, an annular-edged atomizer concentrically nio'unt'ed for rotationon one end of said shaft, said atomiz'er having an extended liquid-guiding surface leading directlyto its annular edgeand including a cylindrical liquid darn projecting from the liquid-guiding surface, a

diggharge. edge lying. closely adjacent to andzequi'distanf 10 StatlOll aI y feed tube extending through saidhollow shaft from the conical interior surface portion of said atomizer; said'sharp' edge being formed by two intersecting surfaces" of the feed device one of which is flat and'lies' substan-* tially normal to the axis of said device; meansfor-rotatirrg and' temiinating in a sharp' annular liquid discharge edge concentric with and-'sp'aced'less than-.05 inch from the extended liquidguiding surface of said atomizer, said feed tube having a knife-edged drip skirt surrounding the said. haft a d atomizer; d means f f edin -liquid 1i") liquid damof-said atomizer, means for rotating said shaft throughsaid feed device and over its liquid dischargeedge' to the interior surface portion of said rotating atomizer;

9. An atomizing apparatus comprising a rotatable-hollow shaft; an annular-edged atomizing'bell concentrically mounted for rotation on one end of said shaft, said-bell having an inner surface flaring outwardly to the annular edge of said bell; agenerally cylindrical liquid darn mounted at one of its ends within the inner surface of said bell concentrically with the axis of said bell with the other end of saidcylindrical dam-projecting toward the annular edge of said bell; a stationary feed device extending concentrically through said hollow shaft and terminating at one end in a lipped portion having an edge overhanging the projecting end of said'liquid d'am; means for rotating said shaft, bell anddam; and means'for tion'flaring conically at an angle to the axis-of said'shaft of approximately 15"; a cylindrical liquid dam mounted atom of its ends within the inner surface'portion of said 40 bell concentrically with the axis of said 'b'ell with the other end of said cylindrical dam projecting from said inner surface portion; a stationary feed tube extending concentrically through said hollow shaft' andterminating in'alipped portion having a liquid discharge edge over- 4 hanging the projecting edge of said liquid dam; means'for' rotating'said shaft, bell and dam; andmeans-forfeeding liquid to said feed tube for fiow therethrough and over and a tomizerabout their axes, and-means-for feeding liquid 1 at a controlled rate to said :feed 'tubefor 'flowthere through and'over its liquid discharge' edge to the liquid guiding surface of the rotating atomizer to form thereon- 'an expanding liquid film-for atomization from the edge of said atomizer.

l2. Inan' electrostatic-spray coating system, a device for feeding liquid-coating material comprising a rotatable hollow shaft, an annular-edged atomizer concentrically 1 mounted for rotation'on one endof said shaft, saidatomizcr having anextended liquid-guiding: surface leading to its annular edge, a stationary feed tube extending through said hollowshaft and terminating inan annular liquid' discharge edge-spaced fromthe' extended surface of said atomizer, said-discharge edgebeingconcentric-with and substantially'equally'spaced from-the liquid-guiding surface-of said a-tomizer, said feed tube-includingadrip'skirt on the-under side of said feedrtube and surrounded by said discharge: edge, means tfor rotating said shaft-and atomizer abouttheir axes; and means-for feeding liquidat a controlled rate to'said feed tube for fiowtherethrough and overits liquid discharge edge to the liquid-guiding- 442,865 Kinder Dec. 16, 1890 2,607,571 Hession, Jr. Aug. 19, 1952 FOREIGN PATENTS 294,460 GreatBritain July 26, 1928 

